I've been able to verify this very solidly grounded scientific theory only very infrequently. Boiled down, it says that, in spite of the main stimulus that moves a trout to take your fly being the need to eat, it is not the only and sometimes not the most important stimulus. In addition to play, curiosity and voracity stimuli, there is another that, although less well-known, can explain some otherwise unpredictable trout reactions. Astutely used, you can hook some of those impossible trout. I'm talking about the stimulus of competition for food.
Imagine two good-sized trout no more than a couple of yards from each other, feeding very selectively on floating insects. Drop your fly with enough slack line right in the middle of the lane that separates both windows. The theory predicts a high likelihood that one of the two trout, aware of the presence of the other, will rush over to beat the other fish to your fly. Let me know how it works in practice for you.

Those long distances that you sometimes see a trout cover to intercept a fly, probably expending more calories than the fly is worth, may be motivated more by an instinct of competition than for basic nourishment.

Developed and sufficiently verified barely two years ago, this theory says that tailing loops have their place and time, a very interesting and practical type of casts. The most common (but definitely not the only) cause of these snubbed loops is the application of too much power too soon at the beginning of the forward cast. But, if you do the following, you'll have a couple of new casts:

Apply the mentioned power and stop, slightly rotating the wrist outwards (from your body). The result is an accurate left hook.

Again apply the power at the beginning of the forward cast, but, this time, in an absolutely lateral cast. You'll have a nice heap of slack at the end of the line.

I've included this as a theory because it's so surprising and unusual and because it opens a field for experimenting. And because I made a bet with someone years ago that tailing loops would never serve a purpose. I lost.

This theory tries to tear down a very generalized belief that fast, turbulent streams are the most difficult to avoid drag. But a bit of fly-casting technique solves most problems on these types of waters. The theory points out that wide, deep stretches and rivers with sinuous surface currents often present impossible-to-solve situations. A clear argument supports this theory:the surfaces of these stretches, full of hundreds of eddies and a multitude of micro currents and countercurrents, usually caused by abundant riverbed vegetation, are almost undecipherable.
Paradoxically, in these circumstances, the only thing you can do is forget anti-drag casts and lengthen your leader as long as possible with a 7X tippet. This sacrifices accuracy, but whoever can think of something else, please let me know.
Like all good theories, this one has lots of detractors. They should experiment with it more.